Re: [kvm-unit-tests PATCH v2 4/4] x86/access: Try emulation for CR0.WP test as well

[Sean Christopherson <seanjc@google.com>]

On Fri, Mar 31, 2023, Mathias Krause wrote:
> Enhance the CR.WP toggling test to do additional tests via the emulator
> as these used to trigger bugs when CR0.WP is guest owned.
> 
> Link: https://lore.kernel.org/kvm/ea3a8fbc-2bf8-7442-e498-3e5818384c83@grsecurity.net/
> Signed-off-by: Mathias Krause <minipli@grsecurity.net>
> ---
>  x86/access.c | 46 +++++++++++++++++++++++++++++++---------------
>  1 file changed, 31 insertions(+), 15 deletions(-)
> 
> diff --git a/x86/access.c b/x86/access.c
> index ae5e7d8e8892..21967434bc18 100644
> --- a/x86/access.c
> +++ b/x86/access.c
> @@ -1107,27 +1107,43 @@ static int check_write_cr0wp(ac_pt_env_t *pt_env)
>  	 * We load CR0.WP with the inverse value of what would be used during
>  	 * the access test and toggle EFER.NX to flush and rebuild the current
>  	 * MMU context based on that value.
> +	 *
> +	 * This used to trigger a bug in the emulator we try to test via FEP.
>  	 */
> +	for (;;) {

As suggested in patch 2, I'm pretty sure it's easier to use a helper, and have
the print statement react to at->flags.